1. Field of the Invention
The present invention relates to a high efficiency coding apparatus used for the purpose of lowering the transmission rate or recording rate periodically without reducing the picture quality of a video signal when transmitting or recording the video signal.
2. Description of the Prior Art
When coding a video signal, in a still picture, coding within a frame is higher in efficiency than coding within a field, while, in a moving picture, it is known that coding within a field is lower in coding distortion than coding within a frame and is hence enhanced in coding efficiency. Therefore, to enhance the coding efficiency, two types of orthogonal transformations are required, that is, the orthogonal transformation suited to coding within a frame and the orthogonal transformation suited to coding within a field.
In the conventional high efficiency coding apparatus, however, for plural orthogonal transformations, plural orthogonal transforming devices and coding devices corresponding to the plural orthogonal transforming devices were necessary. For example, an orthogonal transforming device for coding within frame and a coding device for coding within frame, an orthogonal transforming device for coding within frame and a coding device for coding within frame are necessary. In particular, the coding device is complicated in processing as compared with the orthogonal transforming device, and hence the hardware scale is increased.